SIP - Software Based VOIP Softphones For Mac

If your Macintosh already has a built-in microphone and adequate speakers, Software Internet Phone (SIP) programs for Mac OS X - along with a VOIP provider such as ViaTalk - US Broadband Phone Service, or Lingo's Unlimited US and international calls - may be all you need. These 'soft phone' SIP applications appear on-screen as a virtual 'physical' phone with display and dial-pad you interact with just as you would a hardware phone. The abilities to record calls, display Caller-ID info and more are great for those who spend all day at their desk and want to manage calls via VOIP onscreen.
CounterPath Software Mac OSX Free SIP Phone - XLite
X-Lite from Counterpath is perhaps the oldest free SIP soft phone program for Macintosh OSX out there: X-Lite is the free version of it's more fully featured voice and video successor which is sold at retail: as eyeBeam. Paired with a VOIP provider subscription and the SIP settings properly configured, X-Lite is a great way to dip a toe into softphone voice call management on your Mac


SIP Communicator is a free cross-platform Mac/Windows/Linux based Audio/Video capable Internet Phone and instant messenger that also supports some of the most popular instant messaging and telephony protocols such as SIP, Jabber, AIM/ICQ, MSN, Yahoo! Messenger, Bonjour, IRC, RSS and soon others like IAX. Based on the SIP protocol, its more than just VOIP software, it is a full communications tool that lets you enjoyfree calls, video conferencing, SMS, chat over many existing protocols.
Best SIP soft phone programs for Mac computers
iSoftPhone is a slick program worth checking out: Works with over 11 US VOIP phone providers including Vonage, FWD - Free World Dialup, CallCentric and more. This is important because having easy setup and configuration with a VOIP calling provider known, tested, built-in makes it a snap to setup and start calling away at dirt-cheap rates.